The present invention relates to a container for transport and storage of bulk material and including an outer load carrying container with lifting loops and at least one opening for filling, and a liner. The invention also relates to a special liner to be used with such container.
For most types of bulk materials for which the container is used, the most practical and economical solution has proved to be an outer load carrying container and a liner whose primary function is to protect the bulk material against moisture and contamination. However, air entrapped in the liner can cause stability problems when containers are stacked during storage. Such instability occurs when containers are stacked in tiers. Any upper container will then float on the air cushion of the container underneath. Such floating effect can cause the stacked containers to topple. As such containers often are stacked four to five tiers high, entrapped air in the liners can be very dangerous. Of course, this danger can be avoided by not stacking the containers, but this will increase the required storage area and make the use of the containers more expensive.
To solve this problem different methods have been tried. One method is to try to remove the air by suction from the liner after filling, and another method is to vibrate the container during filling to more densely pack the contents. Even a combination of such methods does not solve the stability problem when stacking containers in storage, as there still will be some air entrapped in the liners which can form air cushions.
A method of perforating liners or wall material is known from the 50 kg sack industry to obtain a stable pallet of 50 kg sacks. Entrapped air in the sack will bleed off through the perforation when the next sack is placed thereon. Palletized loads of 50 kg sacks are always covered with a plastic hood of some sort to avoid penetration of moisture through the perforations of the liners or wall material. To perforate the liners of flexible intermediate bulk containers eliminates instability when stacking containers in storage, but will require covering of the complete stack or each individual container to avoid moisture ingress. Thus, the solution of one problem creates a new one.
The correct positioning of the liner inside the container is important to limit the amount of air which can be trapped inside the liner. However, in practice it is found that during filling of bulk material into the container, problems may arise with the liner, even though it originally has been positioned correctly in the load carrying container. The liner may be displaced and crumpled so that the bulk material filled into the container makes it lopsided, thus forming air pockets which are not filled with bulk material during filling. After tying off the liner, bulk material may flow into the air pockets and the air then escapes to the top.
The securing of the liner position inside the container with adhesive tape at several positions will limit but not solve the problem of liner displacement and crumpling. With poor adhesive quality the tapes will come loose, and with high adhesive quality the tapes cause tearing of the liners. Different methods have been proposed in order to attach the liners to the outer bags as it has been difficult to achieve a centered, stable and correct positioning of the liner during the production of the container. A practical solution to this problem is shown in Norwegian patent No. 153,250 corresponding to EP application No. 84,113,352,0. Norwegian patent application No. 85, 2476 seeks to avoid distortion of the liner within the container by a special method for securing the liner to the load carrying container, where the liner is equipped with tabs to attach the liner to the outer load carrying container. The tabs as such are integral prolongations of the liner sides and are formed by equipping the liner with joints or seams spaced from the outer edges of the liner. As a further object is to provide a liner which can be completely waterproof and as no means are described or detailed as to how excess air can bleed off, such proposed solution does not solve the instability problem due to the air cushion formed by entrapped air when stacking containers in tiers. Thus, the above method fits into all other attempts to solve the problems in connection with the use of a liner. It has turned out that the known solutions have not been satisfactory and at best have solved only a few of the above mentioned problems.